Search found 100 matches
- Sat Mar 13, 2021 9:33 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Problem Types
- Replies: 3
- Views: 313
Problem Types
Hello! I'm really confused as to how to use the different forms of the Arrhenius equation when it comes to a problem (i.e. the exponential form vs. the logarithmic version). Does anyone have any tips/problem types that could demonstrate this? The equations get jumbled up in my head when I'm working ...
- Sat Mar 13, 2021 9:29 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Sapling Week 9/10 Question 1
- Replies: 8
- Views: 634
Re: Sapling Week 9/10 Question 1
Hi Sean! The unique rates per product and reactant are based upon stoichiometric coefficients. The inverse of the stoichiometric coefficient multiplied by the change in concentration over time of a particular substance is equal to the overall rate of the reaction. This should also help you relate th...
- Sat Mar 13, 2021 6:38 pm
- Forum: Phase Changes & Related Calculations
- Topic: state properties
- Replies: 13
- Views: 829
Re: state properties
Hi Mary!
While enthalpy does not change for a particular reaction, regardless of pathway, heat for a reaction may change depending on the pathway taken. This means heat is not a state function. It is pathway-dependent.
While enthalpy does not change for a particular reaction, regardless of pathway, heat for a reaction may change depending on the pathway taken. This means heat is not a state function. It is pathway-dependent.
- Sat Mar 13, 2021 6:35 pm
- Forum: General Rate Laws
- Topic: Pseudo Rates
- Replies: 8
- Views: 746
Re: Pseudo Rates
Hi Isis!
The pseudo rate laws are used to help determine the rate constant in situations where there are multiple variables present. Isolating one variable in a psudo rate law can help simplify the total rate law for a reaction, eliminating unknowns. Hope this helps!
The pseudo rate laws are used to help determine the rate constant in situations where there are multiple variables present. Isolating one variable in a psudo rate law can help simplify the total rate law for a reaction, eliminating unknowns. Hope this helps!
- Sat Mar 13, 2021 6:32 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Gibb's Free Energy vs Enthalpy
- Replies: 4
- Views: 293
Re: Gibb's Free Energy vs Enthalpy
Hi Evie, Based on the equation deltaG=deltaH-TdeltaS, we can figure out whether a reaction is spontaneous or not. If deltaG is negative, the reaction is spontanous. Enthalpy, or deltaH, has an impact on this, considering a positive enthalpy indicates an endothermic reaction and a negative enthalpy i...
- Sun Mar 07, 2021 10:51 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Slow Step
- Replies: 21
- Views: 902
Re: Slow Step
Hi Rayna! There are many factors that could impact whether a reaction is considered the "slow step" or "fast step." As you mentioned, activation energy is one of these. Other components that could impact slow/fast is whether the reaction is thermodynamically favored, size of part...
- Sun Mar 07, 2021 10:48 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Explanation of Reaction Progress
- Replies: 3
- Views: 266
Re: Explanation of Reaction Progress
Hi Ashley! Potential energy increases until activation energy of a reaction is reached, since energy cannot be consumed until the reaction proceeds towards reactants. Once the reaction proceeds, potential energy decreases until completion. The specifics of a reaction depend on enthalpy change, but t...
- Sun Mar 07, 2021 10:43 pm
- Forum: General Rate Laws
- Topic: Intermediates
- Replies: 17
- Views: 1503
Re: Intermediates
Hi Isis!
Intermediates cancel out in a balanced reaction, so they cannot be included in the rate law. The reactions couple: the first reaction produces the intermediate and the second one consumes the intermediate as a reactant. Hope this helps!
Intermediates cancel out in a balanced reaction, so they cannot be included in the rate law. The reactions couple: the first reaction produces the intermediate and the second one consumes the intermediate as a reactant. Hope this helps!
- Sun Mar 07, 2021 10:26 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Reaction/Average Rate
- Replies: 13
- Views: 767
Re: Reaction/Average Rate
Hi!
Reaction rate refers to the rate of a reaction at a specific point, also known as instantaneous rate of change. This is where calculus comes into play (derivatives!). However, average rate of the reaction is just delta(conc)/delta(time) for the complete reaction. Hope that helps!
Reaction rate refers to the rate of a reaction at a specific point, also known as instantaneous rate of change. This is where calculus comes into play (derivatives!). However, average rate of the reaction is just delta(conc)/delta(time) for the complete reaction. Hope that helps!
- Sun Mar 07, 2021 10:22 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Chemical Reactions and Temperature
- Replies: 3
- Views: 246
Re: Chemical Reactions and Temperature
Hi Lusin! The rate of chemical reactions depends on temperature, as temperature relates movement of particles with the addition of heat. As collisions increase between molecules, the reaction is able to proceed more quickly towards products. However, it is important to note that factors such as entr...
- Sun Feb 28, 2021 8:19 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Balancing equations
- Replies: 5
- Views: 292
Re: Balancing equations
Hi! Whether you add H+ or OH- after adding H2O to balance the reaction depends on whether the problem indicates a redox rxn occurring in an acidic or basic solution. An easy way to solve these problems is to add the same amount of H2O molecules as moles of oxygen present on the opposite side of the ...
- Sun Feb 28, 2021 8:16 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Reduction Potential Clarification
- Replies: 4
- Views: 282
Re: Reduction Potential Clarification
Hi Isabelle! I was also confused about this at first when I was completing the homework problems. I figured out that even if the reaction is occurring in the reverse, the equation E(cathode)-E(anode) accounts for this difference, and you should not reverse the sign of the reduction potential prior t...
- Sun Feb 28, 2021 12:34 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Eo of Concentration Cell
- Replies: 3
- Views: 208
Eo of Concentration Cell
In lecture, Dr. Lavelle mentioned that Eo of a concentration cell is always 0. I was wondering why this is the case? Also, it would be great if someone could clarify the difference between a concentration cell and a galvanic/voltaic cell for me! Thank you!
- Sun Feb 28, 2021 12:30 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode and Cathode
- Replies: 4
- Views: 267
Re: Anode and Cathode
Hi ChihWei, For these problems, keep in mind that oxidation occurs at the anode and reduction occurs at the cathode. Given a table with standard reduction potentials, the reaction with a higher reduction potential (oxidizing agent/gets reduced) will be the cathode. The reaction with a lower reductio...
- Sun Feb 28, 2021 12:23 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing with H2O/OH-
- Replies: 6
- Views: 360
Re: Balancing with H2O/OH-
Hi Isabelle, I was a bit confused on this concept at first too, but hopefully this helps! First, I balance the amount of oxygens on each side by adding the appropriate amount of H2O on the opposite side of the rxn. Then, I add H+ ions on the side of the equation opposite of the H2O. At this point, I...
- Sun Feb 21, 2021 11:39 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Reversible vs Irreversible Entropy Calculation
- Replies: 5
- Views: 426
Re: Reversible vs Irreversible Entropy Calculation
Hi Anna! Just want to add on that for an irreversible reaction, deltaS(univ)=deltaS(sys), and the entropy of the surroundings does not change. However, for a reversible reaction, deltaS(univ)=0, and therefore deltaS(sys)=-deltaS(surr).
- Sun Feb 21, 2021 11:35 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: adiabatic reactions
- Replies: 6
- Views: 415
Re: adiabatic reactions
For an adiabatic reaction, final temperature = initial temperature. Also note that for such a system, q = 0, and therefore, deltaU must equal w (work due to expansion or compression). Hope this helps!
- Sun Feb 21, 2021 11:33 pm
- Forum: Calculating Work of Expansion
- Topic: Work and Delta V
- Replies: 20
- Views: 2579
Re: Work and Delta V
Yes! In systems with no expansion or compression, there is no work done, so w=0 in these situations. Unless volume is changed, work is not done, and this is referred to as an isochoric system. You can refer to the equations for irreversible and reversible reactions to make this clear.
- Sun Feb 21, 2021 10:10 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Non-spontaneous exothermic reaction
- Replies: 14
- Views: 4588
Re: Non-spontaneous exothermic reaction
An exothermic reaction may be non-spontaneous if the reaction also leads to a decrease in entropy. Once temperature is above a certain point, this means the reaction becomes entropy-driven, causing the reaction overall to have a positive deltaGo. An online example I found of this is the combustion o...
- Sun Feb 21, 2021 10:06 pm
- Forum: Phase Changes & Related Calculations
- Topic: Textbook Problem 4A1 part C
- Replies: 3
- Views: 313
Re: Textbook Problem 4A1 part C
Hi Bronson, A bomb calorimeter is considered an isolated system because neither energy nor matter is exchanged with its surroundings. However, there is no "perfectly" isolated system in nature, because over a long period of time, a bomb calorimeter may lose heat over time. As Dr. Lavelle m...
- Sun Feb 14, 2021 10:20 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: delta U and delta H
- Replies: 8
- Views: 382
Re: delta U and delta H
Hi!
Delta U refers to a change in internal energy, while delta H refers to a change in enthalpy. The two are not interchangeable, since enthalpy is heat energy, but internal energy is a combination of potential and kinetic energies.
Delta U refers to a change in internal energy, while delta H refers to a change in enthalpy. The two are not interchangeable, since enthalpy is heat energy, but internal energy is a combination of potential and kinetic energies.
- Sun Feb 14, 2021 10:14 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Assumption on type of system
- Replies: 13
- Views: 745
Re: Assumption on type of system
I would assume the system is closed! Especially since we have been practicing a lot of internal energy change problems, it would make sense that in the majority of instances, the system would need to be able to exchange energy with surroundings but not necessarily matter.
- Sun Feb 14, 2021 10:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: n in q=nCdeltaT
- Replies: 16
- Views: 793
Re: n in q=nCdeltaT
Hi Trevor!
The n represents moles, however, there is a separate equation for the use of grams, which uses a different value for C. This is referred to as the specific heat capacity. In the example you stated, C refers to molar heat capacity.
The n represents moles, however, there is a separate equation for the use of grams, which uses a different value for C. This is referred to as the specific heat capacity. In the example you stated, C refers to molar heat capacity.
- Sun Feb 14, 2021 10:02 pm
- Forum: Calculating Work of Expansion
- Topic: Conceptual Explanation
- Replies: 3
- Views: 215
Conceptual Explanation
The textbook states an “infinitesimal” increase/decrease in volume of a system, but what is this referring to? I know how to solve problems with reversible and irreversible expansions but I don’t know why it works conceptually. If anyone could give a concise explanation of the difference that would ...
- Sun Feb 14, 2021 10:01 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Internal Energy Confusion
- Replies: 4
- Views: 228
Internal Energy Confusion
I’m confused as to how we know whether internal energy is increasing or decreasing because the wording of problems can be confusing. Does anyone have any tips/examples to demonstrate?
- Sun Feb 07, 2021 5:47 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Sampling hw #4
- Replies: 7
- Views: 404
Re: Sampling hw #4
Hi Funmi! I think another important factor to consider in addition to what others have already mentioned is phase changes! Even if a reaction causes the formation of products which are multi-atom, energy must enter the system in some of these scenarios to cause that product to form in the first plac...
- Sun Feb 07, 2021 5:44 pm
- Forum: Phase Changes & Related Calculations
- Topic: Endo vs. exo & bond strenghts
- Replies: 8
- Views: 394
Re: Endo vs. exo & bond strenghts
Hi Jacquelyn, To some degree; if the total bond enthalpies (or strengths) on one side of the equation are much greater than the other side, this is the determining factor in whether a reaction is exothermic or endothermic. However, no, there is no quick trick solely depending on bond strengths that ...
- Sun Feb 07, 2021 5:40 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond breaking and forming
- Replies: 11
- Views: 374
Re: Bond breaking and forming
Hi Daniela! This may sound a bit tedious, but writing down the lewis structures for both products and reactants and then writing down every single bond that occurs on either side, eliminating those in common, and then calculating the difference in enthalpies is the most foolproof way in my opinion! ...
- Sun Feb 07, 2021 5:38 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: solving for q (grams vs mol)
- Replies: 5
- Views: 207
Re: solving for q (grams vs mol)
Hi Sandra!
I think whether you can use moles or grams entirely depends on the question, which will impact what constant you can use. I think something that helps is to look at other characteristics of the problem such as constant volume/ideal gas/expansion, to make that determination!
I think whether you can use moles or grams entirely depends on the question, which will impact what constant you can use. I think something that helps is to look at other characteristics of the problem such as constant volume/ideal gas/expansion, to make that determination!
- Sun Feb 07, 2021 5:36 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Capacity of Calorimeter
- Replies: 7
- Views: 989
Heat Capacity of Calorimeter
I'm very confused by the concept of the heat capacity of a calorimeter. Could anyone provide some examples to explain this concept. It showed up a couple times in the Sapling HW, but I'm still not sure how to find it/what it means.
- Sun Jan 31, 2021 10:05 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: percent protonation/deprotonation
- Replies: 15
- Views: 887
Re: percent protonation/deprotonation
Hi Nina, I'm a little confused on this concept as well, but I believe the difference is whether an acid or base is dissociating. Deprotonation refers to when an acid is dissociated and releases H3O+ into a solvent. Percent deprotonation is [H+]/[HA] x 100. Protonation refers to when a base is dissoc...
- Sun Jan 31, 2021 9:41 pm
- Forum: Phase Changes & Related Calculations
- Topic: Salt
- Replies: 19
- Views: 726
Re: Salt
Hi Jordan, If you're asking whether an ionic salt is acidic or basic in general, there is no one answer. Table salt is neutral, because both Na+ and Cl- are spectator ions, so they do not contribute to pH. They are also both the conjugates of a strong base and strong acid. To figure out whether salt...
- Sun Jan 31, 2021 9:08 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Temperature Change
- Replies: 16
- Views: 841
Re: Temperature Change
Hi Rose, The K value increases for an endothermic reaction because heat is net-added to the system for the reaction to occur. When heat increases, the production of products can be increased in comparison. It helps to think of heat as a reactant in this case. When writing out the equilibrium constan...
- Sun Jan 31, 2021 9:03 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Diatomic molecules standard enthalpy of formation
- Replies: 22
- Views: 1331
Re: Diatomic molecules standard enthalpy of formation
Hi Jazlyn, Yes, the standard enthalpy of formation for naturally diatomic molecules should be 0. In general, any element that is in its natural state at 25 degrees Celsius should have an enthalpy of formation of 0. Keep in mind, this rule only applies for single elements and not multi-elemental mole...
- Sun Jan 31, 2021 8:59 pm
- Forum: Phase Changes & Related Calculations
- Topic: Adding/Subtracting Enthalpy of Vaporization
- Replies: 7
- Views: 612
Adding/Subtracting Enthalpy of Vaporization
In one of the textbook sections for the midterm, there were examples in which bond enthalpy was used to calculate standard enthalpy of the reaction. I'm specifically confused about the ones involving phase changes (for example, knowing when to add/subtract enthalpy of vaporization in addition to bon...
- Sun Jan 24, 2021 9:40 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Inert Gases and Le Chatelier's Principle
- Replies: 6
- Views: 520
Re: Inert Gases and Le Chatelier's Principle
As long as the volume of the chamber isn't changed, the inert gas does not change partial pressures involved in the reaction! By definition, inert gases do not react, so their presence does not impact equilibrium in any way (essentially the premise that they would even be a reactant is incorrect). R...
- Sun Jan 24, 2021 9:34 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: figuring out whether salts are acidic or basic
- Replies: 4
- Views: 210
Re: figuring out whether salts are acidic or basic
Hi Jaden, Pulling H+ from the water simply means the base in water is producing OH-, although some bases have a hydroxide group on them, such as K(OH) and Li(OH). Remember, the typical dissociation equation for bases is: [B] + [H2O] --> [BH+] + [OH-]. This is a good representation of how the base &q...
- Sun Jan 24, 2021 9:24 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Determining the Predominant Species
- Replies: 5
- Views: 1392
Re: Determining the Predominant Species
Hi Elena, Sapling gives a really helpful diagram for determining predominant species, and it would be definitely worth it to screenshot/draw out the diagrams they give in the hints! For an acid: if pH < pKa - the neutral species is predominant; if pH > pKa - the charged (basic) species is predominan...
- Sun Jan 24, 2021 9:20 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Determining Acid Dissociation
- Replies: 2
- Views: 92
Re: Determining Acid Dissociation
Hi Isabel! Acids or bases release an OH- or H3O+. In the homework for this week, all acids were specified as monoprotic, and bases were given as amines. This means each acid/base only produces a single OH- or H3O+ in the balanced reaction. The general dissociation equations look like: [HA] + [H2O] -...
- Sun Jan 24, 2021 9:07 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Reversible Reaction
- Replies: 5
- Views: 278
Re: Reversible Reaction
Hi Nathan,
Forward enthalpy and "backward" enthalpy of a reaction are different. The arrow points in one direction to specify which direction the given enthalpy applies to. The given enthalpy would not work for the reverse reaction. I hope this helps!
Forward enthalpy and "backward" enthalpy of a reaction are different. The arrow points in one direction to specify which direction the given enthalpy applies to. The given enthalpy would not work for the reverse reaction. I hope this helps!
- Mon Jan 18, 2021 2:11 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K small or big
- Replies: 5
- Views: 322
Re: K small or big
Hi Zihan, I'm also not sure why this is the case, but I'm assuming it is because there needs to be a significant enough difference (whatever the threshold may be) for a reaction to be considered strongly-product favored or strongly-reactant favored. Any values in between these aren't extreme enough ...
- Mon Jan 18, 2021 2:09 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table- What increases and what decreases
- Replies: 3
- Views: 175
Re: ICE Table- What increases and what decreases
Hi Eileen, Depending on what the problem is asking for, the concentration of the product or reactant may go down. Typically, whatever the reaction starts with will decrease and the compounds on the opposite side of the equation increase. For example, if an experiment begins with the reactants, this ...
- Mon Jan 18, 2021 2:06 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Quotient
- Replies: 12
- Views: 973
Re: Quotient
Hi Matthew!
Q is similar to K, in that the equation setup for both are identical, however, the concentrations that are substituted into the equations are different. Q is when the concentrations of the reactant and product are not at equilibrium. K always uses equilibrium constants.
Q is similar to K, in that the equation setup for both are identical, however, the concentrations that are substituted into the equations are different. Q is when the concentrations of the reactant and product are not at equilibrium. K always uses equilibrium constants.
- Mon Jan 18, 2021 2:04 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Ka and Kb relationship
- Replies: 5
- Views: 226
Re: Ka and Kb relationship
Hi Elena!
Ka and Kb are inversely proportional because Ka*Kb=Kw (10^-14). Because both are on the same side of this equation, one must increase if the other decreases and vice versa.
Ka and Kb are inversely proportional because Ka*Kb=Kw (10^-14). Because both are on the same side of this equation, one must increase if the other decreases and vice versa.
- Mon Jan 18, 2021 2:03 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Getting two positive x values when using quadratic
- Replies: 43
- Views: 4827
Re: Getting two positive x values when using quadratic
Hi Nicole! Although you can get two positive x values when using the quadratic equation, typically one of the values will be too large and cause a concentration to become a negative (which is not possible). In general, test out both values, but the value that keeps the concentration positive is corr...
- Sun Jan 10, 2021 6:25 pm
- Forum: Ideal Gases
- Topic: partial pressures
- Replies: 14
- Views: 426
Re: partial pressures
Partial pressures are the molar fraction of a gas over total pressure in a container (from adding up the total moles of gas in the reaction). I believe in all of the examples concerning equilibrium, the total pressure is 1 atm.
- Sun Jan 10, 2021 6:00 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K vs Kc
- Replies: 9
- Views: 459
Re: K vs Kc
Hi Stephanie! I am a bit confused by your question, as K is referring to an equilibrium constant and Kc simply specifies that the equation uses concentrations. Assuming you're asking how to convert between Kc and Kp, you use the formula Kp = Kc (RT) ^delta(n), where delta(n) represents moles of gas ...
- Sun Jan 10, 2021 5:53 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Left vs. Right
- Replies: 29
- Views: 1074
Re: Left vs. Right
The two terms are very similar. However, shift right/left is referring to a situation in which equilibrium is disturbed and the reaction quotient Q moves in the direction of K. This is Le Chatelier's principle. Saying a reaction favors the left/right is referring to the value of K itself, and whethe...
- Sun Jan 10, 2021 5:49 pm
- Forum: Ideal Gases
- Topic: inert gas and pressure changes
- Replies: 9
- Views: 391
Re: inert gas and pressure changes
Due to Le Chatelier's principle, the equilibrium constant does not change when additional gas is added in a reaction, however, Q, or the reaction quotient does change. The reaction will then move in the direction required for Q = K. Equilibrium constants for gases vary based on temperature!
- Sun Jan 10, 2021 5:47 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Stable Reactants and Products
- Replies: 7
- Views: 246
Re: Stable Reactants and Products
Hi Anna! I believe the term stability refers to concepts from 14A. Based on the chemical structure, IMFs, etc. of the reactants and products, one side of the reaction may be more favorable than the other.
- Thu Dec 17, 2020 12:30 am
- Forum: Lewis Acids & Bases
- Topic: Acid and Base theories
- Replies: 2
- Views: 267
Re: Acid and Base theories
All three types of acid-base theories are valid, but different in scope! I believe one of the UA's mentioned this in her review session -- the definitions are more broad to less broad in the order: Lewis --> Bronsted-Lowry --> Arrhenius. This is logical since the Lewis definition simply discusses th...
- Thu Dec 17, 2020 12:26 am
- Forum: Amphoteric Compounds
- Topic: Amphoteric and Amphiprotic
- Replies: 2
- Views: 398
Re: Amphoteric and Amphiprotic
Hi Aimee! While the definitions of amphoteric and amphiprotic are very similar, they are not identical. Note that all amphiprotic substances are amphoteric, although all amphiprotic substances may not be amphoteric. This is because amphoteric substances simply have to be able to react with acids and...
- Thu Dec 17, 2020 12:24 am
- Forum: Limiting Reactant Calculations
- Topic: General Limiting Question
- Replies: 9
- Views: 892
Re: General Limiting Question
Hi Blake!
While the limiting reactant does determine how much product will be formed, note that this is the theoretical yield rather than the actual yield. The actual yield is almost always below the theoretical yield, since not all reactants convert into products regardless of calculations.
While the limiting reactant does determine how much product will be formed, note that this is the theoretical yield rather than the actual yield. The actual yield is almost always below the theoretical yield, since not all reactants convert into products regardless of calculations.
- Tue Dec 15, 2020 1:12 pm
- Forum: Student Social/Study Group
- Topic: Study music
- Replies: 59
- Views: 6568
Re: Study music
This sounds like an odd recommendation, but the Mario Kart Study Playlist on Spotify is my go to! Video game music helps with my concentration a lot and I would suggest listening to it if you find yourself checking your phone every 5 minutes while studying. I'm sure there's some science behind it :&...
- Tue Dec 15, 2020 1:08 pm
- Forum: Student Social/Study Group
- Topic: Changing Study Habits
- Replies: 35
- Views: 1408
Re: Changing Study Habits
I definitely think something I could have improved personally this quarter is doing the homework for the corresponding lectures as they come out. Instead of having consistent practice with the material, I used homework as a test review, while I think doing it along with lecture content each week wou...
- Sun Dec 06, 2020 10:25 pm
- Forum: Naming
- Topic: Coordination Compound vs complex ion
- Replies: 4
- Views: 2974
Re: Coordination Compound vs complex ion
Hi Rose! Complex ions are charged molecules with a central metal atom. These central atoms are attached to ligands with coordinate covalent bonds (bonds in which both electrons come from the same donor atom). On the other hand, coordination compounds are neutral molecules that have complex ions as a...
- Sun Dec 06, 2020 10:19 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Anion Stabilization
- Replies: 4
- Views: 248
Re: Anion Stabilization
Hi Farah! Compounds are more stable when electrons are far apart. This means highly electronegative anions would pull lone pair electrons further away than other ions, allowing them to become delocalized.
- Sun Dec 06, 2020 1:35 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Ligand Types
- Replies: 3
- Views: 188
Re: Ligand Types
Hi Shannon! Mono/di/tri/polydentate refers to the number of regions available on a ligand to bond to a central atom. These are areas with lone pairs, for example. However, I am also confused on how to easily identify ligands and determine their type. I'm assuming drawing out the Lewis structures of ...
- Sun Dec 06, 2020 1:31 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Sapling #3 pt. 2
- Replies: 5
- Views: 266
Re: Sapling #3 pt. 2
I believe coordination compounds typically have 2, 4, or 6 electron dense regions, and VSEPR shapes that align with these are the most stable for those compounds (specifically when the shape generates some form of symmetry). Seesaw is a very asymmetrical shape, so I'm assuming that is why it is less...
- Sun Dec 06, 2020 1:15 pm
- Forum: Naming
- Topic: Suffixes for Ligands
- Replies: 1
- Views: 195
Suffixes for Ligands
Hi, I'm confused on how to name certain components of ligands. I know that iron, for example, is called ferrate, but how come in compounds like Fe(CN)6 -3, the ligand is ferricyanide and similarly, in Fe(CN)6 -4 the ligand is ferrocyanide? Will we need to know when a compound's common name and ligan...
- Sun Nov 29, 2020 8:33 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Distinguishing Shape from # of Bonds
- Replies: 3
- Views: 117
Re: Distinguishing Shape from # of Bonds
Hi Meghan! From the coordinate number, I'm assuming Dr. Lavelle would want us to identify molecular geometry and not electron geometry. While electron geometry is determined by lone pairs (and we wouldn't be able to magically derive the name from steric number), the coordinate number alone is enough...
- Sun Nov 29, 2020 8:28 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: ions
- Replies: 8
- Views: 432
Re: ions
Hi Andreas!
Charge doesn't have anything to do with VSEPR in terms of shape and molecular geometry. However, charge can influence polarity of bonds and of a molecule overall!
Charge doesn't have anything to do with VSEPR in terms of shape and molecular geometry. However, charge can influence polarity of bonds and of a molecule overall!
- Sun Nov 29, 2020 8:23 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Linear Shape and Lone Pairs
- Replies: 8
- Views: 685
Re: Linear Shape and Lone Pairs
Hi Talia! Yes, it is possible to have a linear shape with lone pairs. Note, however, this is molecular geometry, as opposed to electron geometry! Electron geometry is directly affected by lone pairs, while molecular geometry is not. Check out this link to learn more: https://sciencing.com/difference...
- Sun Nov 29, 2020 7:44 pm
- Forum: Hybridization
- Topic: Counting for Hybridization
- Replies: 2
- Views: 105
Counting for Hybridization
I understand that we count the number of bonding "groups" instead of individual bonds when determining hybridization, but can anyone explain why this is the case? It doesn't make sense to me intuitively that a double bond + single bond on a central atom would have the same hybridization as...
- Sun Nov 29, 2020 7:42 pm
- Forum: Hybridization
- Topic: Double Bond Type
- Replies: 4
- Views: 262
Re: Double Bond Type
Hi Talia! A double bond can't be two pi bonds because of the type of orbital overlap required to form a bond. While sigma bonds are formed from direct end-to-end overlap, pi bonds are formed from side-by-side overlap. Sigma bonds create a stronger bond.
- Sun Nov 22, 2020 11:41 pm
- Forum: Sigma & Pi Bonds
- Topic: Delocalized pi Bonds
- Replies: 2
- Views: 119
Re: Delocalized pi Bonds
Hi Hayden! I believe pi bonds can get delocalized as lobes overlap to form this kind of bond. This leads to electrons flowing freely between multiple atoms. I don't think this impacts the stability of the bond, since sigma bonds are direct, localized covalent bonds.
- Sun Nov 22, 2020 11:24 pm
- Forum: Hybridization
- Topic: Confusion on Hybridization
- Replies: 1
- Views: 105
Confusion on Hybridization
I've been seeing a couple examples of hybridization where a particular molecule has more than one hybridization type, and I'm confused. How is this possible? Is there a particular rule to know when to assign which orbital/the multiple orbital types to particular bond?
- Sun Nov 22, 2020 10:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: How to determine/remember molecular shape?
- Replies: 4
- Views: 231
Re: How to determine/remember molecular shape?
Hi! For me personally, something that has been really helpful is memorizing the different shapes and creating mnemonic devices/acronyms. Then, I practice writing the VSEPR chart with these acronyms. For example: L TP B TH TPy B TB S T L O SPy SP T L It helps more when written down, but this is my so...
- Sun Nov 22, 2020 10:51 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Defining VSEPR Theory
- Replies: 4
- Views: 223
Re: Defining VSEPR Theory
VSEPR theory is a method by which we can better understand molecules' structures, which can help when scientists want to optimize reactions, for example. Molecular geometry can impact how a compound interacts with its environment. VSEPR specifically takes into account the amount of electron "cl...
- Sun Nov 22, 2020 10:35 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma & Pi Bonds General Question
- Replies: 2
- Views: 62
Re: Sigma & Pi Bonds General Question
I would assume we will need to know the differences between sigma and pi bonds in-depth later on, but as of right now, just know that a single bond is a sigma bond, and any bonds greater than one have (n-1) pi bonds. To my knowledge, sigma bonds are directly responsible for a covalent bond, while pi...
- Sun Nov 15, 2020 9:30 pm
- Forum: Octet Exceptions
- Topic: Octet Exceptions Question
- Replies: 5
- Views: 305
Re: Octet Exceptions Question
Expanded octets can have more than 4 bonds! You can look at phosphorous pentachloride as an example (it has 5 bonds). However, even expanded octets don't typically go beyond 5 bonds (Z=10), so don't draw an unlimited number of bonds just because the atom has d-orbitals!
- Sun Nov 15, 2020 9:21 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: dipole moments
- Replies: 10
- Views: 373
Re: dipole moments
Follow Dr. Lavelle! The arrow should be pointing towards the negative dipole, because it indicates where electrons are being pulled.
- Sun Nov 15, 2020 9:16 pm
- Forum: Electronegativity
- Topic: Partial vs Formal charge
- Replies: 8
- Views: 1044
Re: Partial vs Formal charge
Partial charges are usually referred to as dipoles! This is what we are referring to when discussing dipole-ion/dipole-dipole interactions. Partial charges indicate which atom has the electrons closest or furthest away (remember electronegativity!), giving those atoms similar properties as an ion wi...
- Sun Nov 15, 2020 9:12 pm
- Forum: Lewis Structures
- Topic: Bonding with Atoms in the D State
- Replies: 4
- Views: 108
Re: Bonding with Atoms in the D State
Hi! y=Yes, for elements with d-orbitals, you can use an expanded octet (although this usually doesn't go beyond Z=10). Using an extra lone pair would be appropriate in this case. The diagram you drew is one of the resonance structures for sulfur dioxide! The other two options are placing a formal ch...
- Sun Nov 15, 2020 9:07 pm
- Forum: Lewis Structures
- Topic: Brackets
- Replies: 9
- Views: 598
Re: Brackets
To my understanding, enclosed brackets indicate overall charge! While certain atoms within the molecule may have their own formal charges, a bracket is placed around a complete ion's Lewis structure with its overall charge.
- Sun Nov 08, 2020 10:02 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Covalent Bonds with Ionic Character/Polar
- Replies: 3
- Views: 196
Re: Covalent Bonds with Ionic Character/Polar
Covalent compounds with strong ionic character are polar covalent bonds. They are the midway point between nonpolar covalent and ionic bonds. In these types of compounds, electrons will have a "dipole moment" towards the atoms with higher electronegativity, and electrons are shared unequal...
- Sun Nov 08, 2020 9:58 pm
- Forum: Octet Exceptions
- Topic: Expanded Octets
- Replies: 6
- Views: 176
Re: Expanded Octets
Expanded octets are possible for elements with d-orbitals! This means certain elements, such as chlorine and phosphorous, have the ability to fill electrons up to the s2p6d2 state. These typically won't go beyond 10 electrons.
- Sun Nov 08, 2020 9:54 pm
- Forum: Lewis Structures
- Topic: nitrate lewis structure
- Replies: 7
- Views: 1089
Re: nitrate lewis structure
Two oxygen double bonds doesn't work for nitrate because we want to ensure that the most stable version of the structure is being formed. Having a 5 bond nitrogen would break the octet rule, because nitrogen doesn't have a d-orbital to accommodate more valence electrons. This is why instead, a forma...
- Sun Nov 08, 2020 9:44 pm
- Forum: Electronegativity
- Topic: polyatomic ions
- Replies: 4
- Views: 242
Re: polyatomic ions
Polyatomic ions' charges typically follow patterns based on their respective families in the periodic table, although there are exceptions depending on the bond formed. Like Mohamed mentioned, oxygen is almost always -2, unless it is bonding with one of the exceptions. Copper, iron, and a couple oth...
- Sun Nov 08, 2020 9:22 pm
- Forum: Ionic & Covalent Bonds
- Topic: electron configuration
- Replies: 3
- Views: 192
Re: electron configuration
Hi! Orbitals are filled from lowest to highest energy levels. Although the 4s-block is technically has a higher n-value, it has a lower energy level than the 3d-block. A good trick to remember the order in which orbitals are filled (rather than memorizing) is writing a list as follows and drawing ar...
- Sun Nov 01, 2020 10:46 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Orbitals and Subshells
- Replies: 3
- Views: 175
Re: Orbitals and Subshells
Hi! The relationship you mentioned is flipped: orbitals are inside subshells. Orbitals are just ways to describe how electrons align/are distributed for a certain atom, but keep in mind that no one knows what electrons actually look like. Subshells and orbitals are just a mathematical/visual represe...
- Sun Nov 01, 2020 9:50 pm
- Forum: Trends in The Periodic Table
- Topic: Atomic Radius of Ions
- Replies: 2
- Views: 1480
Atomic Radius of Ions
I was wondering how to determine the atomic radius of ions that are non-isoelectronic...I'm confused as to what should be prioritized when organizing the radii in this case. For example, when comparing Na+ and Ca2+, would the high effective nuclear charge of Na+ be prioritized or the larger atomic w...
- Sun Nov 01, 2020 9:31 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Noble Gas Configuration
- Replies: 13
- Views: 555
Re: Noble Gas Configuration
Either method is appropriate to represent the ground state electron configuration of noble gases, although arguably, as you mentioned, putting just the noble gas would be vague. I'm sure if a question as you mentioned came up in a test, Dr. Lavelle would specify whether to write the short-hand or co...
- Sun Nov 01, 2020 9:27 pm
- Forum: Trends in The Periodic Table
- Topic: Radius trends for elements like Carbon
- Replies: 4
- Views: 154
Re: Radius trends for elements like Carbon
Hi Emam! If you are asking about carbon's electronegativity, carbon has a somewhat high electronegativity. It is very unlikely to lose electrons or gain electrons and create an ionic bond, although in CO2, electrons have an attraction towards oxygen, which has a higher electronegativity than carbon....
- Sun Nov 01, 2020 9:16 pm
- Forum: Trends in The Periodic Table
- Topic: Isoelectronic Ions
- Replies: 5
- Views: 205
Re: Isoelectronic Ions
Hi Chloe! As the other comments above have mentioned, isoelectronic ions are ions with the same electron configuration, although their properties may be completely different due to their chemical composition. Something you should be aware of is that the effective nuclear charge (Z-eff) of these ions...
- Sun Oct 25, 2020 11:14 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: N reaching infinity
- Replies: 3
- Views: 508
Re: N reaching infinity
The "infinity" level is theoretical! From my understanding, if the level were to reach infinity, it would just mean the electron is as far as possible from the nucleus as chemically possible, while (just barely) being a part of the atom. I would assume n=infinity could be approached, but n...
- Sun Oct 25, 2020 9:36 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Rydberg Equation - Sapling Question 11
- Replies: 1
- Views: 81
Rydberg Equation - Sapling Question 11
Hi! I'm confused on this Sapling question and would appreciate some help: "A red line is observed at 656.3 nm in the spectrum of atomic hydrogen. Determine the values of n for the beginning and ending energy levels of the electron during the emission of energy that leads to this spectral line.&...
- Sun Oct 25, 2020 9:30 pm
- Forum: Einstein Equation
- Topic: Sapling Homework - electron affinity
- Replies: 5
- Views: 308
Re: Sapling Homework - electron affinity
Yeah I couldn't get the right answer for the second part either. I wonder if there is anything wrong with my conversions. @Samantha, could you explain your steps for the first part and how you got 1.003? I used E=hc/lambda and converted nm to m as well as J to eV, but I still didn't get to 1.003. T...
- Sun Oct 25, 2020 1:07 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Energy Levels
- Replies: 8
- Views: 384
Re: Energy Levels
Hi Will! From my understanding, photons that push electrons over the energy threshold will bounce off the metallic surface in the form of kinetic energy (refer to the work function). I'm also a little confused by your Google search, but I'm assuming that the light is absorbed while energy itself is ...
- Sun Oct 25, 2020 1:00 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Electrons in Orbitals
- Replies: 5
- Views: 198
Re: Electrons in Orbitals
Hi Alen! Electrons like to fill up orbitals in order from lowest to highest energy, in terms of filling up s, p, d, f orbitals. This may be the same reason electrons fill up individual orbitals before completing pairs. Adding on to what Brianne said above, electrons are likely to take up locations t...
- Sun Oct 18, 2020 10:04 pm
- Forum: Photoelectric Effect
- Topic: Short/high wavelength
- Replies: 7
- Views: 297
Re: Short/high wavelength
Regarding the energy threshold, you should refer to the equation E=hv, where E is energy, h is Planck's constant, and v is frequency! Wavelength is not a factor in the energy of a particular beam of light (of course it is indirectly, as frequency and wavelength are inversely proportional), and there...
- Sun Oct 18, 2020 9:48 pm
- Forum: Properties of Light
- Topic: Wave properties of light
- Replies: 4
- Views: 307
Re: Wave properties of light
Light has a couple behaviors that demonstrate it is a wave. These are reflection, refraction, and diffraction! When in contact with new surfaces (or mediums), light interacts and changes. Crash Course Physics has a great video on this: https://www.youtube.com/watch?v=IRBfpBPELmE Also, check out this...
- Sun Oct 18, 2020 4:43 pm
- Forum: Photoelectric Effect
- Topic: What happens to absorbed photons?
- Replies: 6
- Views: 478
Re: What happens to absorbed photons?
Hi Kushaal! You should think of photons as "packets of energy" as Dr. Lavelle mentioned in his lectures. Unlike protons, neutrons, and electrons, photons do not have a mass, but rather, are representations of energy . It would be incorrect to say the photon gets destroyed due to the First ...
- Sun Oct 18, 2020 4:22 pm
- Forum: Properties of Electrons
- Topic: Work Function
- Replies: 2
- Views: 184
Work Function
Hi! I'm a bit confused by the work function, because the function states that E(photon) must be greater than or equal to E(remove electron). How does the "or equal to" make sense in terms of real-world application? If there is no excess energy involved when hitting a metallic surface, it w...
- Sun Oct 18, 2020 4:07 pm
- Forum: Properties of Light
- Topic: Frequency vs Wavelength
- Replies: 22
- Views: 1302
Re: Frequency vs Wavelength
Hi Brianna! Yes, frequency does have an effect on what type of wave something is, because frequency and wavelength are inversely proportional! Each wave type has a unique set of frequencies AND wavelengths that accompany it. Reference the equation c = vλ, where c is a constant ~3.0e8 meters/second. ...
- Sat Oct 10, 2020 3:12 pm
- Forum: Empirical & Molecular Formulas
- Topic: Sapling Q10
- Replies: 4
- Views: 245
Re: Sapling Q10
Hi Ann!
Yes, you disregard the propyl magnesium bromide when calculating for Q10. We aren't concerned about the products from that reactant specifically. Just know that propyl magnesium bromide has 3 carbons to help when balancing equations!
Yes, you disregard the propyl magnesium bromide when calculating for Q10. We aren't concerned about the products from that reactant specifically. Just know that propyl magnesium bromide has 3 carbons to help when balancing equations!
- Sat Oct 10, 2020 3:06 pm
- Forum: Significant Figures
- Topic: What Value to Use for Sig Figs
- Replies: 4
- Views: 178
What Value to Use for Sig Figs
I'm confused as to what value from the problem should be used as a basis for sig figs. For example, if the problem says "Given 5.9 grams of silver and 8.79 grams of gold, what is the expected yield of [some rxn]?" This obviously isn't a real question in the textbook, but I was wondering, h...
- Wed Oct 07, 2020 2:29 pm
- Forum: Empirical & Molecular Formulas
- Topic: Fundamentals Problems: E9
- Replies: 2
- Views: 200
Fundamentals Problems: E9
Hi everyone! I am confused on the following Fundamentals problem, because while the heptahydrate component contains 7 atoms of oxygen, dry Epsom salt is just MgSO4. Should I include the heptahydrate when calculating this answer as well? E.9 Epsom salts consist of magnesium sulfate heptahydrate. Writ...
- Tue Oct 06, 2020 8:35 pm
- Forum: Balancing Chemical Reactions
- Topic: State in chemical reactions
- Replies: 13
- Views: 460
Re: State in chemical reactions
Hi Emily! While writing down the physical state of reactants/products may not be important, knowing the physical states of these molecules is definitely helpful (especially if the question is regarding a precipitation reaction). Visualizing the reaction can help you better understand chemical proces...
- Mon Oct 05, 2020 7:55 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: G5 Molarity of Na
- Replies: 6
- Views: 616
Re: G5 Molarity of Na
Hi Adam! First, convert mass of Na2CO3 into moles. You should get 0.0199 moles Na2CO3. Next, recognize that Na+ and NaCO3 are in a 2:1 ratio (meaning there is 2 mol Na/1 mol NaCO3). If you use dimensional analysis, you should find that 2 mol Na implies 1 mol NaCO3. This means there are 0.0398 moles ...